1. Field of the Invention
The present invention relates to methods and apparatus for the treatment of presbyopia using fiber-coupled lasers to ablate the sclera tissue.
2. Prior Art
Corneal reshaping including a procedure called photorefractive keratectomy (PRK) and a new procedure called laser assisted in situ keratomileusis, or laser intrastroma keratomileusis (LASIK) have been performed by lasers in the ultraviolet (UV) wavelength of (193-213) nm. The commercial UV refractive lasers include ArF excimer laser (at 193 nm) and other non-excimer, solid-state lasers such as those proposed by the present inventor in 1992 (U.S. Pat. No. 5,144,630) and in 1996 (U.S. Pat. No. 5,520,679). The above-described prior arts using lasers to reshape the corneal surface curvature, however, are limited to the corrections of myopia, hyperopia and astigmatism.
Refractive surgery using a scanning device and lasers in the mid-infrared (mid-IR) wavelength was first proposed by the present inventor in U.S. Pat. Nos. 5,144,630 and 5,520,679 and later proposed by Telfair et. al., in U.S. Pat. No. 5,782,822, where the generation of mid-IR wavelength of (2.5-3.2) microns were disclosed by various-methods including: the Er:YAG laser (at 2.94 microns), the Raman-shifted solid state lasers (at 2.7-3.2 microns) and the optical parametric oscillation (OPO) lasers (at 2.7-3.2 microns).
Cornmeal reshaping may also be performed by laser thermal coagulation currently conducted by a Ho:YAG laser (at about 2 microns in wavelength) proposed by Sand in U.S. Pat. No. 5,484,432. This method, however, was limited to low-diopter hyperopic corrections. Strictly speaking this prior art did not correction the true xe2x80x9cpresbyopiaxe2x80x9d and only performed the mono-vision for hyperopic patients. A thermal laser is required and the laser treated area was within the optical zone diameters of about 7 mm.
Ruiz in U.S. Pat. No. 5,533,997 proposed the use of laser ablation of cornea surface to correct presbyopic patients. This prior art, however, must generate multifocal (or bifocal) surface on the central portion of the cornea in order to achieve the desired presbyopia correction. Corneal curvature change by laser ablation in this prior art, however, did not actually resolve the intrinsic problems of presbyopic patient caused where the cornea lens loss its accommodation as a result of loss of elasticity due to age.
All the above-described prior arts are using methods to change the cornea surface curvature either by tissue ablation (such as in UV laser) or by thermal shrinkage (such as in Ho:YAG laser) and all are using lasers onto the central potion of the cornea.
The alternative method for presbyopia correction, therefore, is to increase the accommodation of the presbyopic patients by change the intrinsic properties of the sclera and cililary tissue to increase the lens accommodation without changing the cornea curvature. This method of sclera ablation is fundamentally different from all the prior arts including that of Ruiz, in which reshaping cornea curvature into multifocal shape was required for presbyopia correction.
Correction of presbyopia via the expanding of the sclera by mechanical devices was recently proposed by Schachar in U.S. Pat. Nos. 5,489,299 and 5,354,331. These prior arts all require the implant of external band or using laser heating to affect the position of the insertion band and have the drawbacks of complexity, time consuming, costly and potential for side effects. To treat presbyopia, Schachar""s other U.S. Pat. Nos. 5,529,076 and 5,722,952, proposed the use of heat or radiation on the corneal epithelium to arrest the growth of the crystalline lens by laser coagulation effects. However these two prior arts did not present any details or practical methods and there was no clinical studies have been practiced to show the effectiveness of the proposed concepts.
Roberto Albertazzi et al (Ocular Surgery News, July, 1999) recently proposed to use diamond knife for the incision of the sclera tissue outside the limbus rings to increase the space for sclera expansion. This method however caused corneal bleeding and regression is frequently found after the treatments. We note that there is intrinsic difference between a laser ablation proposed in this invention and the knife incision. The sclera space produced by the incision method is not permanent and may be greatly reduced during the tissue healing and cause the regression. This major source of regression in incision method however will not occur in the laser ablation method as proposed in this invention, where portion of the sclera tissue is permanently removed.
The xe2x80x9cpresbyopiaxe2x80x9d correction proposed by Ruitz (U.S. Pat. No. 5,533,997) using an excimer (ArF) laser also required the corneal surface to be reshaped to form xe2x80x9cmultifocalxe2x80x9d effort for a presbyopia patents to see near and far. However, Ruitz""s xe2x80x9cpresbyopiaxe2x80x9d correction is fundamentally different from that of the present patent which does not change the corneal curvature. The presbyopia correction proposed in the present patent is to increase patient""s accommodation rather reshaping the cornea into xe2x80x9cmultifocalxe2x80x9d surface.
The technique used in the prior art of Bille (U.S. Pat. No. 4,907,586) required a quasi-continuous laser having pulse duration less than 10 picoseconds and focused spot less than 10 micron diameter and the laser is confined to the interior of a selected tissue to correct myopia, hyperopia or astigmatism. Bille also proposed the laser to focused into the lens of an eye to prevent presbyopia. This prior art system is very complicate and needs a precise control of the laser beam size and focusing position. Furthermore, clinical risk of cataract may occur when laser is applied into the lens area.
Treatment of presbyopia by cold lasers was recently proposed by the present inventor in U.S. Pat. application Ser. Nos. 09/189,609 and 09/391,503. These pending patents, however, require the use of a scanning device to generate the laser ablation patterns on the cornea. These systems therefore involve with complicated hardware and software for scanning patterns and patient centration or eye movement is critical.
Accordingly, there is a strong need to treat presbyopia via laser ablation of the sclera tissue using a laser system which may be delivered by a hand held fiber unit. Furthermore, the system may be used in either non-contact or contact modes with laser beam spot sizes defined by the size and shapes of the fiber tips. System proposed in the present patent will be safer than that of prior arts because the central portion of the cornea remains intact and only the area outside the limbus will be ablated by the laser. It is yet another objective of the present patent is to provide a no-invasive method where the conjunctiva layer may be lifted to generate the xe2x80x9cgapxe2x80x9d for fiber tip to insert into the gap and ablate the desired patterns underneath and to avoid or minimize bleeding or infection.
The preferred embodiments of the basic surgical lasers of the present invention shall include: (a) infrared (IR) lasers having wavelengths range of about (1.4-3.2) microns including but not limited to solid state lasers of Er:glass, Ho:YAG, Er:YAG, Er:YSGG, infrared gas lasers, solid-state lasers converted by optical parametric oscillation (OPO); (b) ultraviolet (UV) lasers having wavelength range of about (190-355) nm, such as ArF (at 193 nm) and XeCl (at 308 nm) excimer lasers and solid-state lasers using frequency conversions; (c) semiconductor diode lasers at about 980 nm, (1.3-1.55) microns, and (1.8-2.1) microns; (d) diode-pumped solid state lasers having wavelength range of about (190-355) nm and (2.7-3.2) microns such as diode-pumped Er:YSGG, Er:YAG, Nd:YAG, Er:glass and Ti:saphire laser and their harmonic generation.
It is yet another preferred embodiment is to couple the basic lasers by a fiber and deliver the laser beam to the treated area of the eye by a handheld piece which is further connected to a fiber-tip at various shapes.
It is yet another preferred embodiment to focus the laser beams into a desired spot size on the treated area of the eye. Various ablation patterns may be generated manually via the fiber-connected hand piece including multiple rings of spots and radial line incisions outside the limbus.
It is yet another preferred embodimentis to open the conjunctiva layer prior to the laser ablation of the under-layer of the sclera tissue for a better control of the ablation depth and for safety reasons. It is yet another preferred embodiment is that the conjunctiva layer may be lifted to generate the xe2x80x9cgapxe2x80x9d for fiber tip to insert into the gap and ablate the desired patterns underneath and to avoid or minimize bleeding or infection.
Further preferred embodiments of the present invention will become apparent from the description of the invention which follows.